When you are alone, you are not with any other people. 独自的
adjective [原级]独自的;单独的;孤独的,无依无靠的;唯一的
If one person is alone with another person, or if two or more people are alone, they are together, without anyone else present. 独处的 Exercising alone can be boring.
adverb [方式副词]独自,单独;独力,单干(地);单,只;仅仅…就
Bringing up a child alone should give you a sense of achievement. 独力一人养大一个孩子会给你一种成就感。